The present invention relates to an improved optical switch device with a rolling shutter in which, when the shutter is in an open position, light passes impinges on a substrate of the device, and when the shutter is in a closed position, light is reflected back by the shutter.
Optical switch devices have been developed in which a movable shutter is mounted on a smooth flat substrate. The shutter is positioned such that light is directed toward the substrate in proximity to the shutter. The shutter is made of a thin material which has stresses introduced such that the shutter is normally in a coiled configuration. As a result, light directed onto the substrate is able to pass through the substrate without obstruction from the shutter. When a voltage is applied across the substrate and the shutter, the resulting electric field causes the shutter to uncoil into a flat position over the surface of the substrate. Light directed onto the substrate therefore impinges on the uncoiled shutter. Such a device can be implemented in a variety of optical switching applications.
For example, U.S. Pat. No. 5,233,459, issued on Aug. 3, 1993, entitled xe2x80x9cElectric Display Device,xe2x80x9d describes an optical switch device with a movable shutter. The shutter is formed on a glass substrate such that when the shutter is coiled up, light can pass freely through the device. When the shutter is uncoiled, it is held in a relatively flat state over the substrate by the electric field applied between the shutter and the substrate. In this state, light impinges of the shutter.
Such devices are prone to several drawbacks. For example, the shutter can have a tendency to stick to the substrate. When the electric field is removed or reduced, the sticking interferes with the ability of the shutter to recoil. This can cause substantial delays in devices and processes which utilize the device, or can result in complete failure of the devices and processes. Also, the gaseous atmosphere in which the device operates can slow the opening and closing of the shutter, also resulting in delayed processing. Also, the shutter can tend to distort when it is uncoiled.
The present invention is directed to an improved optical switch device or element, an array of optical switch devices or elements and an optical switching method. The optical switch device of the invention includes a substrate and a flexible membrane or shutter attached at one of its ends to a surface of the substrate. The substrate includes an optical port portion on which light can be made to impinge. The flexible membrane is attached to the substrate in proximity to the optical port portion of the substrate. The flexible membrane is configured such that it is controllable between a first or closed state and a second or open state. In the closed state, the membrane is disposed onto the substrate over the optical port portion such that when light is directed toward the optical port portion of the substrate, the light impinges on the flexible membrane. In the open state, the membrane is disposed away from the optical port portion of the substrate such that when light is directed toward the optical port portion, it impinges on the optical port portion.
In one aspect of the invention, a reflective surface or mirror is formed on the flexible membrane. In this configuration, when the membrane is in the closed state, light is reflected by the mirror. In the open state, light is allowed to impinge on the optical port portion of the substrate.
The flexible membrane or shutter is configured such that it is normally in the open state. When the membrane is fabricated, stresses are introduced into the material such that in a quiescent state, the membrane is rolled up into a coiled configuration. When the membrane is attached to the substrate, and a programming or operating voltage is applied across the membrane and the substrate, the resulting electric field causes the membrane to uncoil and lay over the optical port portion of the substrate. Generally, as long as the voltage is applied, the membrane is held in the uncoiled closed state. When the voltage is removed, the membrane coils back up into the open state.
In one aspect of the invention, an aperture or hole is formed through the substrate at the optical port portion of the substrate. In this configuration, when the membrane is in the open position, light directed at the optical port portion of the substrate passes through the aperture without obstruction. As in the general configuration set forth above, when the membrane is in the closed position, the light impinges on the membrane.
In accordance with another aspect of the invention, the device includes a latching capability which allows the membrane to be held in the closed, i.e., uncoiled, state without maintaining the operating voltage applied across the substrate and the entire membrane. The device can be provided with a latch electrode formed on the substrate at the end of the membrane opposite the attachment end when the membrane is uncoiled. When the membrane is uncoiled, the end of the membrane is brought into close proximity to the latch electrode on the substrate. After the membrane uncoils into the closed position by application of the operating voltage, a latching voltage is applied across the latch electrode and the membrane. The resulting electric field in the air gap between the end of the membrane and the substrate holds the membrane in the uncoiled state. The operating voltage can then be removed. Since an electric field only exists where there is no contact between the membrane and the substrate, sticking of the membrane to the substrate is reduced or eliminated.
This latching feature provides several advantages. The latch feature substantially relieves degraded performance or failure of devices caused by sticking of the membrane to the substrate. Without the latching feature, the operating voltage would be maintained across the entire membrane and the substrate to keep the entire membrane in contact with the substrate as long as the switch remained in the closed state, in some cases for long periods of time. In such cases, the membrane often sticks to the substrate, resulting in significant degradation in performance or complete failure of the device. Because in the present invention, the membrane is maintained in the closed position by electric field in the air gap between the membrane and the substrate only the latch electrode, the probability of sticking is virtually eliminated.
In another aspect of the invention, the membrane is provided with a plurality of slits. The slits relieve strain in the membrane and prevent distortion of the membrane when it is pulled down over the substrate. The reduced or eliminated distortion allows the reflective surface on the membrane to be maintained extremely flat, resulting in greatly improved performance.
Another set of slits can be provided to enhance the switching performance of the device. Because the device of the invention operates in a gaseous atmosphere, atmospheric effects can slow the operation of the device. This second set of slits is provided to allow the gaseous atmosphere to pass through the membrane as it moves, i.e., as it transitions between states. Because the slowing effects of the atmosphere are greatly reduced by these gas venting slits, the device can change states faster, resulting in improved speed and performance.
In another aspect of the invention, the membrane is provided with a plurality of dimples, also to reduce sticking of the membrane to the substrate when the operating voltage is removed to transition the switch device from the closed state to the open state. The dimples provide much smaller points of contact between the membrane and the substrate. Holes can be additionally fabricated in the electrodes in the area around the dimples. This has the effect of reducing the electric field in the area of the dimple. As a result, the probability of the membrane sticking to the substrate is substantially reduced.
In another aspect of the invention, a raised annular rim is provided around the optical port portion of the substrate. When the membrane is uncoiled over the optical port, the area of the membrane near the port contacts the rim. The has the effect of flattening the membrane which improves performance of the device when the reflective surface is attached to the top of the membrane.
In another aspect of the invention, another approach is employed to flatten the membrane and/or mirror. The attachment edge of the membrane, i.e., the edge of the membrane at which the membrane is attached to the substrate, is made shorter than the rest of the width of the membrane by forming the membrane with a tapered shape. This has the effect of reducing distortions in the membrane and thereby allows the membrane to lay flat when it is held in the uncoiled or closed position.